Humidity Probe for Contrail-Cirrus Avoidance

Our proposal provides a measurement technology to detect atmospheric conditions that favor the formation and persistence of aircraft-induced cirrus clouds in real time. These clouds account for the major share of aviations climate impact via radiative forcing. We need aircraft equipped with our technology that fly along the busiest flight corridors combined with adaptive flight routing as mitigation strategy. We are developing a new compact laser-spectroscopic instrument to measure the relevant humidity levels. During Phase I we achieved a relative uncertainty of 110 ppb (0.11 ppm) for real-time data recorded at 1 Hz with a short optical pathlength of only 30 cm. With further data averaging the relative uncertainty improved to ~25 ppb (0.025 ppm) for 1-minute averages. We have demonstrated excellent linearity of response of our Phase I benchtop system between 10 ppm and 6000 ppm. Based on simulated vertical profile measurements in the laboratory we estimate the accuracy of our Phase I benchtop system to be 1..2 ppm or ~2 %, whichever is greater. This performance makes our technology highly suitable for the proposed contrail avoidance application onboard aircraft. In Phase II we will further refine the instrument design with a strong focus on manufacturability and low cost. Innovations include an optical-fiber based open-path-free optical system with collimation optics and detector integrated into the sample cell, and a fast and efficient look-up based spectroscopic fit. We are actively planning the demonstration of the Phase II prototype instrument during an aircraft deployment. We propose an accurate measurement based on direct-absorption laser spectroscopy technology to detect atmospheric humidity conditions to inform several scientific questions, including: the formation and persistence of aircraft-induced cirrus clouds. With our sensor, humidity can be measured with high accuracy in situ and in real time onboard commercial aircraft. The data can be used as feedback for contrail-cirrus avoidance strategies. Aircraft-induced contrail-cirrus clouds account for the major share of aviation’s climate impact by way of radiative forcing. It is therefore critical to minimize the occurrence of contrails and contrail cirrus to reduce the climate impact of the global aviation fleet. This requires aircraft that fly on intercontinental routes along the busiest flight corridors to be equipped with our technology to minimize the climate impact of aviation. During Phase I of this project, we have successfully demonstrated the feasibility of the spectroscopic measurement approach. Our results include high precision of 0.11 ppm at 1 Hz and high linearity at contrail-relevant humidity as well as during simulated vertical profiles. In Phase II we will develop our benchtop system into a fully operational ultra-compact, autonomous, and maintenance-free instrument to measure humidity onboard research and commercial aircraft. Our Phase II main objectives are to (1) design and develop the instrument optics, electronics and software, and packaging; (2) confirm and refine the instrument performance during laboratory experiments; (3) operate the instrument onboard a research aircraft for demonstration and validation against existing humidity-measurement technology. During Phase II of this project, we will deliver the following: (1) Design of the instrument prototype optics, electronics and software, and packaging; (2) Deploy and validate the instrument onboard a research aircraft; (3) Two instrument engineering prototypes for independent tests by NASA.
Benefits: A simple-to-integrate, highly compact, and maintenance free water vapor instrument for NASA aircraft campaigns would be a great asset for many scenarios. This includes satellite validation where a NASA aircraft would perform profile measurements co-located with satellite observations. The project will enable commercial airspace management procedures that avoid contrail induced cirrus cloud, which has a significant short term climate benefit. Persistent contrail avoidance has emerged as a mitigation strategy for airlines to reduce their climate burden. The sensor enables a global system that quantifies the atmospheric state in real time, where contrails could be avoided with minor adjustments. The additional benefit of the technology developed here will involve assimilation of the water data by meteorological modeling systems.